Water resistant high amylose corrugating adhesive with improved runnability

ABSTRACT

A water resistant, starch-based, alkaline corrugating adhesive is provided having improved tack or runnability and comprises using a chemically treated or modified high amylose starch having at least 40% by weight amylose content as the raw starch component.

This application is a division of application Ser. No. 08/069,886, filedJun. 1, 1993 now U.S. Pat. No. 5,393,336.

BACKGROUND OF THE INVENTION

This invention relates to a high amylose starch-based, water resistant,alkaline corrugating adhesive with improved runnability or tack. Moreparticularly, this invention is directed to chemically treated highamylose raw starch which is useful in alkaline corrugating adhesives andprovides high levels of water resistance while being operable at highcorrugator running speeds.

The term "corrugated paperboard" as used herein refers to a flutedmedium and a facing adhesively joined to the tips on one or both sidesof the fluted medium. The procedures employed in the production ofcorrugated paperboard usually involve a continuous process whereby astrip of paperboard is first corrugated by means of heated, flutedrolls. The protruding tips on one side of this fluted paperboard stripare then coated with an adhesive, and a flat sheet of paperboard,commonly known in the trade as a facing, is thereafter applied to thesetips. By applying heat and pressure to the two paperboard strips thusbrought together, an adhesive bond is formed therebetween. Theabove-described procedure produces what is known to those skilled in theart as a single-faced board in that the facing is applied to only onesurface thereof. If a double-faced paperboard in which an inner flutedlayer sandwiched between two facings is desired, a second operation isperformed wherein the adhesive is applied to the exposed tips of thesingle-faced board and the adhesive-coated tips are then pressed againsta second facing in the combining section of the corrugator under theinfluence of pressure and heat. The typical corrugating process and theoperation and use of corrugators in general are described in U.S. Pat.Nos. 2,051,025 and 2,102,937 issued on Aug. 18, 1936 and Dec. 21, 1937respectively to Bauer.

A major concern in such processes is the selection of the appropriateadhesive, as its properties will affect not only the strength andstability of the final corrugated product, but also the parameters, suchas corrugator speed, within which the process can be operated. Thus,such adhesives are chosen in light of the specific requirements of theprocess and the properties desired in the ultimate corrugatedpaperboard. The adhesives most commonly used in corrugating arestarch-based adhesives which are popular because of their desirableadhesive properties, low cost and ease of preparation.

The most fundamental of starch corrugating adhesives is an alkalineadhesive which is comprised of ungelatinized raw starch suspended in anaqueous dispersion of cooked starch (carrier). The adhesive is producedby gelatinizing starch in water with sodium hydroxide (caustic soda) toyield a primary mix of gelatinized or cooked carrier, which is thenslowly added to a secondary mix of raw (ungelatinized) starch, borax andwater to produce the fully formulated adhesive. In the corrugatingprocess, the adhesive is applied (usually at between 25° and 55° C.) tothe tips of the fluted paper medium or single-faced board, whereupon theapplication of heat causes the raw starch to gelatinize, resulting in aninstantaneous increase in viscosity and tack and formation of theadhesive bond.

It is often desired or necessary in the manufacture of corrugatedpaperboard that the adhesive yield water resistant bonds which canwithstand extended exposure to high humidity, water, melting ice and thelike. A number of approaches have been devised to produce waterresistant corrugating adhesives. One method involves preparation of anacidic, starch-based adhesive wherein urea-formaldehyde together with anacidic catalyst is added to the composition to produce water resistantbonds in corrugated board. Another more commonly followed methodinvolves the use of alkaline curing starch-based adhesive whereinthermosetting resin such as urea-formaldehyde, ketone-formaldehyde orresorcinol-formaldehyde are added as crosslinking additives to producewater resistant bonds.

In recent years, due to the uncertainty of the safety of formaldehyde,efforts have been made to reduce the levels of exposure to formaldehydeor even better, to provide a formaldehyde-free alkaline starch-basedadhesive composition which is useful in the manufacture of corrugatedpaperboard.

While water resistance is an important factor to be considered informulating a corrugating adhesive, another property which must beconsidered and is directly related to the utility of the formulation isits ability to rapidly form an initial bond, termed "tack" or "greenbond strength". This rate of tack development is directly related to thespeed at which the corrugator can be run, i.e., runnability, andconsequently there exists a need for corrugating adhesives possessinghigh green bond strengths and rapid development of tack.

While there are different theories regarding the respective roles of theraw starch and the carrier in the development of adhesive properties,some research has centered on the view that the carrier contributes tothe bond strength and setting speed of the adhesive. Indeed, it has beensuggested that good tack in the carrier leads to good tack (andtherefore improved runnability) in the adhesive (see e.g., R. Williams,C. Leake and M. Silano, TAPPI, Vol. 60, No. 4, Apr. 1977, pp. 86-89).Further, it has been known for many years that a corrugating adhesivewhose carrier portion is prepared from a high amylose starch exhibitssuperior tack to one prepared from pearl starch, which contains about27% amylose, because the high amylose carrier will have improvedrheological and film-forming properties, and also increased moistureresistance particularly when used with chemical crosslinkers.Consequently, there are many different carriers available for use instarch-based adhesives.

To date, however, relatively little experimentation has been done withthe raw (uncooked or ungelatinized) starch portion of the adhesive,other than varying the species of starch source utilized. While highamylose starch, as noted above, has been used in the carrier portion ofthe adhesive to provide improved water resistance and tack, it has notbeen found to be useful in the raw starch because of its added expenseand more significantly, because it does not provide the level of tack orrunnability desired. This is noted in U.S. Pat. No. 3,532,648 issued onOct. 6, 1970 where it is disclosed that by varying the secondary(unpasted) starch (i.e., ungelatinized or raw starch) employed, theproperties of the adhesive can advantageously be tailored to theparticular corrugated-based production requirements. The patent thendiscloses that when an amylose component (at least 35% by weight) isadded to a given formulation to provide at least a portion of thesecondary starch (raw starch), the waterproofness of the adhesive isimproved but such improvement is accompanied by a decrease in themachine speed of the adhesive, depending on how much amylose componentis used.

Accordingly, the need still exists for a formaldehyde-free alkalinestarch-based adhesive that has good water resistance properties and alsohas an improved and satisfactory degree of tack or runnability that willmake it particularly useful in corrugating paperboard manufacturingoperations.

SUMMARY OF THE INVENTION

It has now been found that a starch-based, water resistant alkalinecorrugating adhesive free of formaldehyde and other crosslinkingadditives and having improved tack or green bond strength is obtainedwhen a chemically treated or modified high amylose starch is used as theungelatinized raw starch component. This high amylose containingadhesive has high levels of water resistance and improved runnabilitymaking it especially useful in high speed corrugator operations.

More particularly, this invention is directed to a starch-based alkalinecorrugating adhesive comprising an aqueous dispersion of a cooked orgelatinized starch and a raw starch which is a chemically treated ormodified high amylose starch, i.e., at least 40% by weight amylosecontent. This corrugating adhesive, which has good water resistance andimproved runnability or tack as evidenced by its green bond strength,results from the use of high amylose raw starch which has been mildlytreated or modified by oxidation, hydrolysis, esterification,etherification, crosslinking, and alkali or solvent treatment.

DETAILED DESCRIPTION OF THE INVENTION

The alkaline corrugating adhesive composition of this inventioncomprises an ungelatinized raw starch, a cooked carrier starch, analkali base material and water.

The ungelatinized raw starch component utilized in this invention iscomprised in whole or in part by a chemically treated or modified highamylose starch containing at least 40% and preferably at least 50% byweight of amylose content.

As previously noted, the use of high amylose starch as the raw componentof corrugating adhesives has not provided the level of tack orrunnability desired. While not wishing to be bound by theory, it isbelieved that chemical treatment or modification of high amylose starchas described herein, has in some way weakened or disrupted the granularstructure of the starch and/or increased the ability of the granule toswell and absorb water. This in turn results in an adhesive having anincreased rate of tack development and green bond strength and providesimproved runnability and the ability to operate at higher corrugatorspeeds with no reduction in water resistance.

The chemical treatment or modification of the higher amylose starch toweaken or disrupt the granular structure involves one or more operationsincluding oxidation, hydrolysis, esterification, etherification,crosslinking, and alkali or solvent treatment. While each of these stepshave been utilized in the treatment of various starches, it is importantthat the chemical treatment or modification of high amylose starch asused herein only involves a mild or low treatment level or degree ofapplication. This allows the high amylose starch to satisfactorilyperform as the raw starch component in a corrugating adhesive whileproviding good water resistance and improved tack or runnabilityproperties. Furthermore, and significantly, it eliminates the use offormaldehyde or other chemical additives needed to provide waterresistance.

Oxidation using alkaline hypochlorite and more particularly sodiumhypochlorite is a preferred treatment for the high amylose starch. Thisis carried out using a light oxidation of 0.1 to 1.5, more preferably0.2 to 1.2% by weight available chlorine under alkaline conditions, pHof 7.5 to 12. While hypochlorite is a preferred and well known oxidizingagent, other known oxidants such as hydrogen peroxide, persulfate,peracetic acid and permanganate as well as combinations of permanganateand hydrogen peroxide as disclosed in U.S. Pat. No. 4,838,944 issued onJun. 13, 1988 to L. Kruger may be used.

Hydrolysis by acid treatment with e.g. concentrated HCl at 0.1 to 1% byweight is also useful in the chemical treatment or modification of highamylose starch. Besides hydrochloric acid, other acids and particularlymineral acids such as sulfuric acid and phosphoric acid may also beused.

Treatment of starch under alkaline conditions is also useful in thechemical treatment and modification of high amylose starch. Sodiumhydroxide, at 2 to 4% by weight treatment, is a preferred alkalinematerial but alkali metal hydroxides such as potassium hydroxide,alkaline earth hydroxides such as calcium hydroxide, alkaline earthoxides such as barium oxide, alkali metal carbonates such as sodiumcarbonate, and alkali metal silicates such as sodium silicate may alsobe used.

Another treatment technique for disrupting the amylose granularstructure involves the use of solvents such as dimethyl sulfoxide andother polar, aprotic solvents, e.g. N-methyl pyrrolidone and dimethylformamide, and aliphatic alcohols. Particularly useful is dimethylsulfoxide diluted with other solvents such as aliphatic alcohols orhalogenated hydrocarbons such as chloroform. The solvent is typicallyadded in a sufficient amount, e.g. 1.5 to 15 parts per part by weight ofstarch and then the mixture is refluxed.

Besides the treatments noted above, chemical modification of the highamylose starch can be made by esterification, etherification orcrosslinking using known procedures but at low treatment levels.Esterification, for example, may involve acetylation with aceticanhydride or formation of the half-esters of dicarboxylicacids/anhydrides at 0.5 to 3% by weight treatment levels. Etherificationmay involve modification with alkylene oxides such as ethylene oxide andpropylene oxide or carboxymethylation with e.g., sodium chloroacetate,at treatment levels of 0.5 to 3% by weight. Crosslinking may involvemodification, for example, with multifunctional reagents such asepichlorohydrin, phosphorus oxychloride, trimetaphosphates, anddicarboxylic acid anhydrides at treatment levels of 0.005 to 0.1% byweight. The various treatments and modifications as disclosed herein arefurther described in Starch:Chemistry and Technology, edited by R. L.Whistler, et al., Chapters X and XVII, 1984 and ModifiedStarches:Properties and Uses, edited by O. B. Wurzburg, Chapters 2-6, 9and 11, 1986.

While the various treatments of high amylose as described above can beused alone, they may also be combined, such as treatment with dimethylsulfoxide in combination with hypochlorination in order to obtaindesirable properties.

The high amylose starch material used in this invention as the rawstarch component and optionally as the carrier component is onecontaining at least 40% by weight of amylose. It is well known thatstarch is composed of two fractions, the molecular arrangement of onebeing linear and the other being branched. The linear fraction is knownas amylose and the branched fraction amylopectin. Starches fromdifferent sources, e.g. potato, corn, tapioca, and rice, etc., arecharacterized by different relative proportions of amylose andamylopectin components. Some plant species have been generally developedwhich are characterized by a large preponderance of one fraction overthe other. For instance, certain varieties of corn which normallycontain about 22-28% amylose have been developed which yield starchcomposed of over 40% amylose. These hybrid varieties have been referredto as high amylose or amylomaize.

High amylose corn hybrids were developed in order to naturally providestarches of high amylose content and have been available commerciallysince about 1963. Suitable high amylose starches useful herein are anystarches with an amylose content of at least 40% and preferably at least50% by weight. While high amylose corn starch has been especiallysuitable, other starches which are useful include those derived from anyplant species which produces or can be made to produce a high amylosecontent starch, e.g., corn, peas, barley and rice. Additionally, highamylose starch can be obtained by separation or isolation such as thefractionation of a native starch material or by blending isolatedamylose with a native starch.

The high amylose starch used in the raw starch component as describedherein, may comprise the entire starch portion of that component or itmay comprise a blend of 10% or more, preferably 25% or more and morepreferably 50% or more by weight of chemically treated or modified highamylose starch with other starches suitable for use in corrugatingadhesives. These other starches as well as the starch in the carriercomponent may be selected from the several starches, native orconverted, heretofore employed in starch corrugating adhesivecompositions. Suitable starches include, for example, those starchesderived from corn, potato, waxy maize, sorghum, wheat and the carriermay also include high amylose starches i.e. having 40% or more by weightof amylose. Modified starches and various derivatives such as ethers,esters, thin-boiling types prepared by known processes such as mild acidtreatments, oxidation, etc., and other starches typically employed incorrugating may be used. Other starches which may be used as the carrierstarch include the high amylose starches having greater than 60% byweight amylose as disclosed in application docket no. 1458, filed on thesame date as this application and entitled "All Natural, Starch-Based,Water Resistant Corrugating Adhesive", which is incorporated herein byreference.

The ratio of raw starch to carrier will vary depending on propertiesdesired and generally will range from about 2:1 to 16:1 by weightdepending on the nature of the starch and the viscosity desired. Thetotal amount of starch employed including the gelatinized or cookedcarrier and the ungelatinized raw starch will typically be in the rangeof about 10 to 50% by weight, based on the weight of the composition

While the corrugating adhesive composition as described herein isprimarily directed to the particularly preferred embodiment of acomposition comprising a carrier starch and a raw starch, it may alsoinclude a no carrier composition having just a single starch componentcomprising an ungelatinized starch which upon subsequent treatment withalkali becomes partially swollen. This single starch composition willcomprise the chemically treated or modified high amylose starch of thisinvention, optionally with blends of other starches as described herein.The total amount of starch employed in the single starch componentcomposition (no carrier) will range from about 10 to 50% by weight,based on the weight of the composition. Other components including thealkali, boron-containing salt and water will be used in amounts asotherwise described herein.

The adhesive composition also includes an alkali which is used inamounts sufficient to provide the adhesive with a pH greater than 7,more particularly from about 7.5 to 13 and preferably from 10 to 13.Typically this represents an amount of from about 0.3 to 5% andpreferably from about 1 to 4% by weight based on the weight of starch.

The alkali (base) employed herein is preferably sodium hydroxide;however, other bases may be used in partial or full replacement of thesodium hydroxide and include, for example, alkali metal hydroxides suchas potassium hydroxide, alkaline earth hydroxides such as calciumhydroxide, alkaline earth oxides such as barium oxides, alkali metalcarbonates such as sodium carbonate, and alkali metal silicates such assodium silicate. The alkali may be employed in aqueous or solid form.

Another common ingredient of corrugating adhesives is a boron-containingsalt, e.g., borax which is useful as a tackifier and which is optionallyused in amounts of up to about 5% by weight, based on the total weightof starch. Additionally, any conventional non-chemically functionaladditives may be incorporated into the adhesive in minor amounts, ifdesired. Such additives include, for example, preservatives; defoamers;wetting agents; plasticizers; solubilizing agents; rheology modifiers;water conditioners; penetration control agents; peptizers such as urea;gelatinization temperature modifiers; inert fillers such as clay andfinely ground polymers; thickeners such as inorganic colloidal clays,guar, hydroxethyl cellulose, alginates, polyvinyl alcohol, polymers ofethylene oxide and the like; colorants; and emulsions such as polyvinylacetate.

The remainder or balance of the adhesive composition will be water in anamount of from about 40 to 90% and preferably about 50 to 80% by weight,based on the total weight of the adhesives.

In the preparation of the corrugating adhesives herein, the method usedby the practitioner can vary without serious consequences. Ordinarily,however, the carrier starch is first gelatinized (cooked) in a portionof the water with the alkali (caustic soda) to provide the carriercomponent of the adhesive. In a separate vessel, a mixture or slurry ismade of the raw starch, borax (optional) and remaining water. Thecarrier and raw starch mixture are combined to form the final adhesive.Optional ingredients, if desired, can be added at any convenient pointduring the preparation of either component but are usually added to thefinished adhesive.

The adhesives herein can be used to bond single- or double-faced boardsusing any equipment which is presently employed for the preparation ofcorrugated board. Thus, the adhesive is usually maintained at atemperature of between 20 and 55° C. before its application to theprotruding tips of the fluted paper strip. The actual application may beaccomplished by the use of glue rolls which are ordinarily employed inmost corrugating machines, or one may, if desired, utilize otherapplication methods which may be able to achieve a differentdistribution of adhesive. Following the application of the adhesive tothe fluted paper strip, the latter is then brought into immediatecontact with the facing board under the influence of heat and pressure,as is well know in the art. A double-faced board may be subsequentlyprepared by bringing a second facing in contact with the open flutedsurface of the single-faced board by the usual procedures.

Any of the various paperboard substrates may be utilized in combinationwith the adhesive composition of the present invention in order toprovide corrugated paperboard. As the corrugating adhesive of thepresent invention provides water resistant properties, it is usuallydesirable to utilize a water resistant paperboard in combination withthe adhesive in order to provide a water resistant corrugated paperboardproduct. One preferred paperboard product is a wax impregnatedpaperboard, however, any of the various water resistant paperboardproducts such as, e.g., resin impregnated paperboard, may be utilized incombination with the water resistant adhesive of the present invention.

In the following examples, which are merely illustrative of the variousembodiments of this invention, all parts and percentages are given byweight and all temperatures are in degrees Celsius unless otherwisenoted.

The following test procedures were used to evaluate the variousadhesives and starches herein used in preparing corrugated board.

BRABENDER PEAK VISCOSITY

A Brabender alkaline solution containing 0.86% sodium hydroxide and0.74% 10 mole borax was used to slurry the starch sample. A 350 cmgsensitivity cartridge was used. To a 32 g anhydrous sample of starch wasadded the caustic/borax Brabender solution to a total charge weight of460 g. The mixture was slurried and placed in a Brabender cup and thesample heated to 30° C. and held for five minutes, then heated at 1.5°C./minute to 90° C. The peak viscosity in Brabender units (B.U.) wasobserved for each sample.

TACK TEST

Samples of adhesive were examined for tack development and green bondstrength in the joining of a 62 lb/MSF (1000 square fee) wet strengthcorrugating liner to a 33 lb/MSF wet strength corrugating medium.

The adhesive was applied to the corrugating liner using a 10 mil Birdapplicator. Subsequently, a sheet of corrugating medium was placed atopa hot plate at 350° F. (177° C.) under a 5 g/cm² weight for 30 seconds.Immediately thereafter, one end of the liner was attached to a dial-typespring scale. The medium was then manually separated from the liner in acontinuous fashion and the force required to achieve such separation wasperiodically recorded. This force is a measure of the green bondstrength and the rate of tack development with time and is related tothe speed at which a corrugator can be run, i.e., the higher the greenbond strength and the faster tack is developed, the faster thecorrugator can be run.

WATER RESISTANT PROPERTIES

Sample adhesives were evaluated for the water resistant properties ofbonds formed on double-faced corrugated paperboard using the followingmethod which simulates conditions of the double-back section of acorrugator.

The adhesive sample was applied at 3 mil thickness with a Birdapplicator to a glass plate and was transferred to sheets of asingle-face web of 62 lb/1000 ft ² (0.302 kg/m²) wet strength liner and33 lb/1000 ft ² (0.147 kg/m²) wet strength medium by means of directhand pressure. The single-face samples were then placed on top ofanother sample of the wet strength liner and the resultant double-facedboard was bonded at 0.25 psi on a hot plate at 177° C. for 5 seconds.The bonded boards were then placed in a conditioning atmosphere of 22°C., 50% relative humidity for 24 hours, after which dry 2×4 inch samplesand additional 2×4 inch samples of the boards placed in water at 22° C.for 24 hours were tested as described below.

The sample boards were evaluated for dry pin adhesion and wet pinadhesion using the tests described in TAPPI Standard T 821 OM-87 using aHinde and Dauch Crush Tester obtainable from Testing Machines Inc.,Mineola, N.Y. The test results were recorded in pounds (per 8 squareinches) required to separate completely the double-face liner from thesingle face web. The results are the average of six replicate trials.

STEIN-HALL VISCOSITY

Viscosities were determined using a conventional Stein-Hall cup andmeasuring the time in seconds, required for 100 ml of the adhesivecomposition to pass through an orifice having a diameter of 3/32 inch.

BROOKFIELD VISCOSITY

Viscosities were determined using a Brookfield Viscometer (model RVT) at20 rpm and 100° F.

EXAMPLE 1

Preparation of Adhesive

All samples of corrugating adhesive were prepared in essentially thesame manner, differing only in the precise starches employed and theratios of components. A representative preparation is presented below.

A carrier component was prepared by cooking at 60° C. (140° F.) 65.3 gof high amylose corn starch (70% amylose) in 132 g of water. A total of5.1 g of sodium hydroxide (dissolved in 13.2 g of water) was then addedand the system was agitated for 10 to 20 minutes. Then, 132.0 g of waterwas added to cool the system and quench the reaction.

The raw starch component was prepared in a separate vessel by combining221.6 g of selected treated or other starch with 429.1 g of water atabout 30° C. (90° F.) and adding 3.8 g of borax (pentahydrate) toprovide a slurry which was agitated for five minutes. The carriercomponent was then slowly added and additional water added, if desired,to adjust viscosity. The prepared adhesive was subsequently used in thedifferent test procedures.

EXAMPLE 2

To a slurry of 1 kg of a high amylose corn starch material, (-50%amylose) in 1.5 l of water at 30° C., enough 3% NaOH was added to raisethe pH to 10.8. Sufficient sodium hypochlorite (NaOCl) at 4.84%available Cl₂ was added to provide solutions at treatment levels of 0.2,0.4, 0.6, 0.82 and 1.2% available Cl₂ respectively. Each solution slurrywas stirred for 18 hours while the pH was maintained above 10.8 byaddition of 3% NaOH. Excess sodium hypochlorite was neutralized with 10%sodium bisulfite. The pH was adjusted to 6.0 with HCl, the slurryfiltered and washed three times with 1.5 l of water. The alkalineBrabender peak viscosity for each solution was determined and theresults noted as follows:

    ______________________________________                                        NaOCl treatment level                                                                          Alkaline Brabender                                           (% available/Cl.sub.2)                                                                         Peak Viscosity                                               ______________________________________                                        0.0              1500 B.U.                                                    0.2              2710 B.U.                                                    0.4              2900 B.U.                                                    0.6              2590 B.U.                                                    0.82             2000 B.U.                                                    1.2              1545 B.U.                                                    ______________________________________                                    

Samples of each treated solution were then used as the treated highamylose raw starch component in a corrugating adhesive prepared inaccordance with Example 1.

                                      TABLE 1                                     __________________________________________________________________________    RAW STARCH WITH                                 TACK DEVELOPMENT              NaOCl TREATED                                                                             %     STEIN  BROOKFIELD                                                                             GEL           measured                      HIGH AMYLOSE                                                                              STARCH                                                                              HALL   VISCOSITY                                                                              TEMPER-                                                                             DRY WET in grams over time            (50% AMYLOSE)                                                                             IN    VISCOSITY                                                                            20 rpm   ATURE PIN PIN 5  10 15 20 25                (% AVAILABLE Cl.sub.2)                                                                    WATER (sec.) @ 100° F.                                                                       (°F.)                                                                        (lb)                                                                              (lb)                                                                              sec                                                                              sec                                                                              sec                                                                              sec                                                                              sec               __________________________________________________________________________    Untreated   28.5% 81     4050     154   118 17.1                                                                              175                                                                              200                                                                              200                                                                              225                                                                              250               0.2%        27.8% 137    3700     155   129 16.3                                                                              300                                                                              350                                                                              400                                                                              700                                                                              900               0.4%        28.1% 81     3500     154   116 15.8                                                                              250                                                                              375                                                                              375                                                                              650                                                                              975               0.6%        27.8% 75     2920     154   123 18.8                                                                              200                                                                              250                                                                              350                                                                              625                                                                              850               0.82%       28.5% 93     3550     156   133 18.9                                                                              275                                                                              325                                                                              475                                                                              650                                                                              925               1.2%        27.8% 130    3720     152   120 17.7                                                                              300                                                                              325                                                                              500                                                                              625                                                                              800               __________________________________________________________________________

The adhesive samples were then tested for various properties which areshown in Table 1 along with a comparative sample which used untreatedhigh amylose starch (50% amylose) as the raw component. The resultsillustrate the improvement in runnability as shown by the tackdevelopment test of corrugating adhesives containing the NaOCl treatedraw starch over the untreated raw starch.

Additional corrugating test adhesives containing other treatedhigh-amylose raw starch components are shown below.

EXAMPLE 3

Alkaline Treatment of High Amylose Raw Starch

To a slurry of 1 kg of high amylose corn starch (50% amylose) in 1.5 lof water, enough 3% NaOH was added to raise the pH to 11.5. The slurrywas stirred for 18 hours at 45° C. and then filtered and washed twicewith 1.5 l of pH 11.5 water. The alkaline Brabender peak viscosity wasdetermined to be 1860 Brabender units (B.U.). The solution was then usedas the treated high amylose raw starch component in a corrugatingadhesive prepared in accordance with Example 1 and the adhesive testedfor various properties as shown in Table 2.

EXAMPLE 4

Acid Treatment of High Amylose Raw Starch

To a stirred slurry of 1 kg of high amylose corn starch (50% amylose) in1.5 l of water at 52° C., 5.0 g of concentrated hydrochloric acid (0.5%treatment) was added and the slurry stirred for 18 hours. The slurry wasthen neutralized by slowly adding sodium carbonate to raise the pH to4.5 and then 3% NaOH was added to bring the pH up to 5.5. The slurry wasfiltered and washed with 1.5 l of water. The alkaline Brabenderviscosity was determined to be 1260 Brabender units The treated solutionwas then used as the raw starch component in a corrugating adhesiveprepared in accordance with Example 1 and the adhesive tested forvarious properties as shown in Table 2.

EXAMPLE 5

Hydroxypropylation of High Amylose Raw Starch

To a stirred slurry of 15 g NaOH, 90 g of sodium sulfate and 1 kg ofhigh amylose corn starch (50% amylose) in 1.5 l of water, 5.0 g ofpropylene oxide (0.5% treatment) was added. The slurry was sealed andplaced in a tumbler at 40° C. for 18 hours. The pH was adjusted to 5.5with 17.5% nitric acid and the slurry filtered and washed three timeswith 1.5 l of water. The alkaline Brabender peak viscosity wasdetermined to be 1800 B.U. The solution was used as the treated highamylose raw starch component in a corrugating adhesive prepared as inExample 1 and then tested for various properties as shown in Table 2.

EXAMPLE 6

Acetylation of High Amylose Raw Starch

To a stirred slurry of 1 kg of high amylose corn starch (50% amylose) in1.5 l water at pH 8 and room temperature, 20.g of acetic anhydride (2%treatment) was added dropwise. The pH was controlled at 8 by addition of3.0% NaOH and the slurry was then stirred for an additional 30 minutesat room temperature. The pH was adjusted to 5.5 with 9.25% HCl and theslurry was filtered and washed three times with water. The alkalineBrabender peak viscosity was 1800 B.U. This treated starch was used asthe raw starch component in a corrugating adhesive prepared as inExample 1 and tested for various properties with results shown in Table2.

EXAMPLE 7

Carboxymethylation of High Amylose Raw Starch

To a stirred slurry of 1 kg of high amylose corn starch (50% amylose)and 3.95 g of NaOH in 2 l of 95% isopropanol/water, 10 g of sodiumchloroacetate (1% treatment) was added. The slurry was stirred at 50° C.for 18 hours, then neutralized by addition of 5.93 g of acetic acid. Theslurry was filtered and washed three times with 1.5 l of water. AlkalineBrabender peak viscosity was 2020 B.U. The treated starch was used asthe raw starch component of a corrugating adhesive as in Example 1 andthe adhesive tested for various properties shown in Table 2.

EXAMPLE 8

DMSO Treatment of High Amylose Raw Starch

A mixture of 1 kg of high amylose corn starch (50% amylose) and 2.5 1 of60:40 methanol/dimethyl sulfoxide (DMSO) was refluxed for 0.5 hours. Themixture was filtered hot and washed twice with 2 l of methanol followedby 1 l of ethanol. The starch had a fat content reduced from 0.85% to0.06% and an alkaline Brabender peak viscosity of 1900 B.U. The treatedstarch was used as the raw starch component of a corrugating adhesiveprepared as Example 1 and the adhesive was tested for various propertiesshown in Table 2.

EXAMPLE 9

A sample of DMSO treated starch solution prepared in Example 8 wasfurther treated with sodium hypochlorite (NaOCl) by stirring 3 kg of theDMSO treated starch in 4.5 1 of water at 30° C. and adding 3% NaOH toraise the pH to 10.8. To the slurry was added 555.1 g of sodiumhypochlorite at 4.43% available Cl₂ to provide a treatment level of0.82% available Cl₂. The slurry was stirred for 18 hours while the pHwas kept above 10.8 by addition of 3% NaOH. Excess sodium hypochloritewas neutralized with 10% sodium bisulfite. The pH was adjusted to 6.0with 9.25% HCl, the slurry filtered and washed three times with 4.5 l ofwater. The alkaline Brabender peak viscosity was 3000 B.U. and thetreated starch was used as the raw starch component of a corrugatingadhesive as in Example 1 and tested for various properties shown inTable 2.

EXAMPLE 10

To a stirred slurry of 4 g of NaOH and 500 g of high amylose corn starch(50% amylose) in 750 ml of water, 0.04 g of epichlorohydrin (0.008%treatment) was added. The slurry was sealed and placed in a tumbler at40° C. for 18 hours. The pH was adjusted to 5.5 with 9.25% HCl and theslurry filtered and washed three times with 750 ml of water. Thealkaline Brabender viscosity was determined to be 2980 B.U. This treatedstarch was used as the raw starch component in a corrugating adhesiveprepared as in Example 1 and tested for various properties with resultsshown in Table 2.

It will be noted that the test results shown in Table 2 particularlyillustrate the improved runnability of the different treated highamylose starch raw components used in a corrugating adhesive, asevidenced by tack development (green bond strength), as compared to useof an untreated high amylose starch.

                                      TABLE 2                                     __________________________________________________________________________                    STEIN  BROOKFIELD                                                                             GEL            TACK DEVELOPMENT                               HALL   VISCOSITY                                                                              TEMPERA-                                                                             DRY WET measured in grams over                                                        time                           RAW STARCH.sup.1                                                                       % STARCH                                                                             VISCOSITY                                                                            20 rpm   TURE   PIN PIN 5  10 15 20  25                TREATMENT                                                                              IN WATER                                                                             (sec.) @ 100° F. (cps)                                                                 (°F.)                                                                         (lb)                                                                              (lb)                                                                              sec                                                                              sec                                                                              sec                                                                              sec sec               __________________________________________________________________________    Untreated                                                                              28.5   81     4050     154    118 17.1                                                                              175                                                                              200                                                                              200                                                                              225  250              Alkali   27.8   82     3820     157    117 14.4                                                                              275                                                                              315                                                                              400                                                                              425  500              (NaOH) treated                                                                Acid (HCl)                                                                             28.5   86     4000     156    124 18.8                                                                              300                                                                              450                                                                              450                                                                              500  575              Treated                                                                       Hydroxy- 27.8   66     2860     156    126 15.7                                                                              175                                                                              200                                                                              250                                                                              375  450              propylated                                                                    Acetylated                                                                             27.8   73     3250     163    122 17.1                                                                              250                                                                              275                                                                              325                                                                              370  425              Starch Ester                                                                  Carboxy- 28.5   111    4120     150    123 16.4                                                                              200                                                                              350                                                                              450                                                                              500  500              methylated                                                                    Starch Ether                                                                  DMSO/MeOH                                                                              27.8   66     3900     151    129 18.9                                                                              275                                                                              400                                                                              575                                                                              675  700              Treated                                                                       DMSO/MeOH                                                                              27.8   64     3300     155    143 22.0                                                                              300                                                                              425                                                                              525                                                                              675  900              then 0.82%                                                                    NaOCl                                                                         treated                                                                       Epichlohydrin                                                                          27.8   98     3800     154    121 14.6                                                                              325                                                                              450                                                                              800                                                                              1075                                                                              1300              Crosslinked                                                                   __________________________________________________________________________     .sup.1 Raw starch is high amylose corn starch (˜50% amylose)       

EXAMPLE 11

To further illustrate this invention, corrugating adhesives wereprepared using sodium hypochlorite treated high amylose corn starch (50%amylose) and untreated high amylose corn starch (50% amylose) as the rawstarch component. These adhesives were used to prepare 200 Test, C-fluteboard constructed of 42 lb/MSF (1000 sq. ft.) singleface (SF) liner, 26lb/MSF medium and 42 lb/MSF doubleback (DB) liner (42/26/42 boardconstruction) and the performance results given in Table 3. For furthercomparison, a standard adhesive containing corn starch as the rawstarch, Nabond® a high amylose based carrier starch (a product ofNational Starch and Chemical Company) and also containing a waterresistance resin additive Dacrez® 81 (an acetone-formaldehyde condensateproduct of National Starch and Chemical Company) was also used toprepare the C-flute board described above.

The adhesives were prepared by first forming the carrier component bycooking 200 lbs of high amylose corn starch (70% amylose) in 100 gal. ofwater at 135° F. A 50% solution of NaOH in water (2.2 gal.) was thenadded and the system agitated for 5 minutes. Five lbs. of borax (10 m)was added and the system agitated for 20 minutes followed by theaddition of 60 gals. of water to cool the system and quench thereaction.

The raw starch component was prepared in a separate vessel by adding 90gal. of water to the selected raw starch (550 lbs.) at 95° F., andadding 13 lbs. borax (10 m). The carrier compound was then slowly addedto form the adhesive. In the case of the Nabond adhesive, 30 lbs. of thewater resistance resin (Dacrez 81) was post added to the finishedadhesive. The formed adhesives were then used in preparing the 200 test,C-flute board as noted above and the test results given in Table 3.These results indicate a higher degree of water resistance at the 700ft/min corrugating speed for the adhesive using the treated raw starchover both the adhesive with untreated raw starch and the control.

                                      TABLE 3                                     __________________________________________________________________________    200 Test C-Flute 42/26/42 Board Construction                                                  STEIN HALL                                                                            GEL                 WET PIN                                                                             DRY PIN                     RAW STARCH                                                                             % STARCH                                                                             VISCOSITY                                                                             TEMPERATURE                                                                             CORRUGATING                                                                             (lb)  (lb)                        TREATMENT                                                                              IN WATER                                                                             (sec.)  (°F.)                                                                            SPEED (ft/min)                                                                          SF DB SF DB                       __________________________________________________________________________    High amylose                                                                           26.1   38      152       700       5.3                                                                              8.8                                                                              100                                                                              117                      Starch (50%)                                                                  amylose)                                                                      sodium                                                                        hypochlorite                                                                  (NaOCl)                                                                       treated                                                                       High amylose                                                                           26.1   24      153       700       0.0                                                                              6.3                                                                              124                                                                              120                      (50%                              400       5.7                                                                              7.5                                                                               87                                                                              123                      amylose)                                                                      starch -                                                                      untreated                                                                     Corn starch -                                                                          23.1   35      152       600       2.3                                                                              5.6                                                                               84                                                                               94                      untreated.sup.1                                                               __________________________________________________________________________     .sup.1 Included Dacrez 81 a water resistance additive.                   

What is claimed:
 1. In a water resistant alkaline curing corrugatingadhesive having improved tack and green bond strength and comprising ano carrier starch composition containing an ungelatinized raw starchcomponent, the improvement comprising using a chemically treated ormodified high amylose starch having at least 40% by weight amylosecontent as the raw starch component.
 2. The corrugating adhesive ofclaim 1 wherein the chemical treatment or modification of the highamylose starch comprises oxidation, hydrolysis, esterification,etherification, crosslinking, and alkali or solvent treatment.
 3. Thecorrugating adhesive of claim 2 wherein the composition containssufficient alkali to provide a pH of greater than
 7. 4. The corrugatingadhesive of claim 3 wherein the high amylose starch is oxidized bytreatment with alkaline hypochlorite.
 5. A process for preparingcorrugated paperboard having improved tack and green bond strength andcomprising the steps of:a) applying to the tips of the corrugations of afluted paper strip a starch-based, water resistant alkaline curingcorrugating adhesive comprising:1) from about 10 to 50% by weight, basedon the weight of the composition, of starch including the ungelatinizedraw and gelatinized carrier portions of the starch, 2) from about 0.3 to5% by weight, based on the weight of the starch, of an alkali, and 3)from about 40 to 90% by weight, based on the weight of the composition,of water wherein the raw starch is a chemically treated or modified highamylose starch having at least 40% by weight amylose content, and b)applying a facing to the adhesive coated tips of said fluted paper stripto form an adhesive bond.
 6. The process of claim 5 wherein the chemicaltreatment or modification of the high amylose raw starch componentcomprises oxidation, hydrolysis, esterification, etherification,crosslinking, and alkali or solvent treatment.
 7. The process of claim 6wherein the raw starch component comprises a high amylose starchoxidized by treatment with alkaline hypochlorite.
 8. A corrugatedpaperboard product prepared employing a water resistant alkaline curingcorrugating adhesive having improved tack and green bond strength andcomprising an aqueous dispersion of a gelatinized carrier and anungelatinized raw starch component wherein the raw starch component is achemically treated or modified high amylose starch having at least 40%by weight amylose content.
 9. The corrugated paperboard product of claim8 wherein the chemical treatment or modification of the high amylose rawstarch component comprises oxidation, hydrolysis, esterification,etherification, crosslinking, and alkali or solvent treatment.
 10. Thecorrugated paperboard product of claim 8 wherein the raw starchcomponent comprises a blend containing 25% or more by weight of highamylose treated or modified starch with other starch materials and thecomposition contains sufficient alkali to provide a pH of greater than7.